Mechanically-adjustable optical phase filters for modifying depth of field, aberration-tolerance, anti-aliasing in optical systems

ABSTRACT

An optical system with mechanical adjustment provides for the rotation and/or translation of one or more optical phase filters to variably select an extended depth of field, aberration-tolerance, and/or anti-aliasing properties of an optical imaging system. By adjusting the amount of phase induced on the wavefront, a user may select image quality selectively. The system may further automatically counter change of focus and/or aperture to maintain substantially constant image properties. Typically, two phase filters are used and moved concurrently to achieve desired image properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional ApplicationSerial. No. 60/458,299, filed Mar. 28, 2003, and incorporated herein byreference.

BACKGROUND

[0002] Prior art optical design within optical imaging systems hasprimarily focused on optical elements and the detector used to capturean image. Such optical elements typically include lenses and mirrorsthat focus and magnify optical radiation. The detector is, for example,an analog detector (e.g. film) or a digital detector (e.g., CCD or CMOSarray) that detects the optical radiation to render a final image.

[0003] Mechanical adjustment of optical elements is also known in theprior art to control and obtain best focus within optical imagingsystems. The most common method of mechanical adjustment is to vary thedistance of the image plane by moving a lens. Other mechanicaladjustment methods involve interchanging lens elements with differentfocusing power.

[0004] One form of optical focusing through mechanical means involvestransverse movement of two optical elements, as described in U.S. Pat.No. 3,305,294. In the '294 patent, a pair of aspherical optical elementsmoves transversely in equal but opposite displacements. The form of theaspherical optical elements is defined by polynomials that are stronglydependent on the cubic terms of a power series of two variables.

[0005] An improvement to the focusing method in the '294 patent isdescribed in U.S. Pat. No. 3,583,790. The '790 patent allows lateralmovement of only one aspheric optical element as opposed to two asphericoptical elements, as required by the '294 patent.

[0006] Another method of modifying focus is described in U.S. Pat. No.4,650,292. In the method of the '292 patent, two or more asphericaloptical elements are rotated about axes decentered with respect to theoptical axis, to modify focus.

[0007] The aforementioned prior art thus facilitates obtaining bestfocus within the imaging system by using mechanical means. If one of theoptical elements of the imaging system changes, e.g., due to thermalconditions, then the system may lose focus and, unacceptably, the image.Moreover, aside from changes in focal length and aperture, the depth offocus, depth of field and amount of anti-aliasing of the imaging systemremain unchanged. Furthermore, if there is a change of focal lengthand/or aperture, there is no present way, for example, to maintain afixed depth of focus, depth of field and/or anti-aliasing effects, ifdesired.

[0008] The aforementioned patents (U.S. Pat. Nos. 3,305,294; 3,583,790;4,650,292) are incorporated herein by reference.

SUMMARY

[0009] In one aspect, mechanical adjustment of phase filters is providedto modify wavefront phase and extend depth of field (and/or depth offocus) within an optical imaging system. Such mechanical adjustment maymodify the wavefront phase to control aberration-tolerance and/oranti-aliasing properties of the imaging system.

[0010] In one aspect, wavefront phase is modified by movement of phasefilters. In one example, the phase filters are arranged along theoptical axis of the imaging system. Each of the phase filters modifiesthe wavefront phase in a particular way, to encode the wavefront with aphase function. In one aspect, the filters have the same phase functionbut are rotated relative to one another to effect the desired wavefrontphase modification.

[0011] Those skilled in the art will appreciate that mechanicaladjustment of the phase filters may occur in several ways to effect thedesired phase change in the wavefront, without departing from the scopethereof. For example, in one aspect a phase filter is moved transverselyto the optical axis to modify wavefront change as a function of thetransverse movement; such a phase filter has a phase function thataccommodates the transverse movement to effect the desired wavefrontphase modification. In another aspect, a phase filter is rotated throughdifferent parts of the filter to effect wavefront phase modification;such a filter is, for example, a large disc through which the wavefrontpasses, wherein rotation of the disc encodes a new phase function ontothe wavefront.

[0012] In another aspect, an optical imaging system with mechanicaladjustment is provided that is particularly suited for use in digitalimaging systems, such as digital cameras. Specifically, the opticalsystem with mechanical adjustment modifies wavefront phase within theimaging system to effect desired depth of field, aberration-tolerance,and/or anti-aliasing properties. As above, the imaging system employsand selectively moves one or more phase filters to modify wavefrontphase. A detector (e.g., a digital CCD or CMOS array, or analog film) isused to detect electromagnetic radiation after the phase filters. Thiselectromagnetic radiation may take the form of a blurred, intermediateimage. Digital image processing of data from the detector removescertain effects induced by the phase filters to render a final, in-focusimage with the desired properties (i.e., depth of focus, depth of field,aberration-tolerance, anti-aliasing properties).

[0013] In one aspect, the digital image processing may be effectedthrough a digital signal processor which has position information of thephase filters. The position information corresponds to a selected phasemodification of the wavefront that invokes the desired properties. Theselected phase modification is effectively removed during digital signalprocessing to yield the desired imaging properties.

[0014] Accordingly, in one aspect, a user interface provides forselective user phase modification of the wavefront to effect the desiredproperties. The user interface connects with a motor responsive to userinputs to modify wavefront phase in the appropriate way.

[0015] In another aspect, an optical system with mechanical adjustmentfacilitates variably extending depth of field and increasing aberrationtolerance. The system has a first aspheric optical wavefront filter anda second aspheric optical wavefront filter. In one aspect, the first andsecond filters are parallel to one another and substantially share acommon optical axis within the optical system. A means (e.g., a motor)is provided to rotate and/or translate the first optical filter withrespect to the second optical filter. Both the first and second asphericoptical wavefront filters are constructed and arranged to alter theoptical transfer function of the optical system in such a way that thealtered optical transfer function is substantially insensitive toaberrations over a greater range of aberrations than was provided by theunaltered optical transfer function.

[0016] In one aspect, the amount of alteration of the optical transferfunction is chosen by rotating (and/or translating) the first filterwith respect to the second filter, and vice versa. Those skilled in theart appreciate that other movements of the phase filters may be appliedto the wavefront within the optical system to obtain similar functionand modification of the optical transfer function, to obtain the desiredimaging properties.

[0017] In another aspect, the optical imaging system with mechanicaladjustment is configured for imaging an object, and further has (a) adetector that detects an intermediate image of the object and (b) animage processor that processes data from the detector to reverse certaineffects induced by the first and second optical wavefront filters,thereby generating a final image with the desired imaging properties.

[0018] In another aspect, the means to rotate and/or translate the firstand second optical wavefront filters is a motor and control sub-system.The motor and control sub-system may be an automatic motor and controlsub-system that provides mechanical adjustment of the wavefront phase toeffect desired imaging properties (e.g., depth of focus,aberration-tolerance, anti-aliasing effects).

[0019] In one aspect, user input may be supplied to optical system via auser interface for controlling the means to rotate and/or translate theoptical filters, for example to selectively control focusing of opticalsystem and/or aberration reduction therein.

[0020] In still another aspect, the optical system with mechanicaladjustment has a non-linear analog image detector, such as photographicfilm. The non-linear analog image detector, after detecting an image ofthe object, is scanned or sampled and values are linearized to removethe non-linear input/output characteristics of the detector. Then, thepost processing element processes the linearized image by reversingalteration to the optical transfer function of the optical systemaccomplished by the first and second optical wavefront filters.

[0021] The method of another aspect facilitates variably affecting thewavefront phase of an optical system to selectively extend depth offield and/or increase aberration tolerance by a variable amount. Themethod includes the steps of aligning one or more aspheric opticalwavefront filters in the optical system, and moving the opticalwavefront filters to alter phase of the wavefront. In one aspect, themethod further includes the step of capturing the wavefront with adetector and processing data from the detector to reverse certaineffects induced by the wavefront filters, to generate a final image withthe desired image properties (e.g., depth of focus,aberration-tolerance, anti-aliasing). For example, in one aspect, theoptical wavefront filters modify an optical transfer function of theoptical system such that the altered optical transfer function issubstantially insensitive to aberrations over a greater range ofaberrations than was provided by the unaltered optical transferfunction.

[0022] In still another aspect, the motor and controller changes theaperture of the optical imaging system (e.g., by adjusting a motorizedaperture within the system). In and of itself, the aperture change canaffect the imaging properties (e.g., depth of focus, depth of field,aliasing properties, aberration tolerance) of the optical system—whichmay not be desired. Accordingly, the motor and controller mayadditionally move the optical filter(s) so as to modify phase of thewavefront, to readjust the imaging properties so that they remainunchanged even with the change of aperture size. In this way, forexample, one can maintain a depth of field in object space irrespectiveof a change of aperture.

[0023] In another aspect, the motor and controller changes the focallength of the optical imaging system (e.g., by moving a lens of thesystem). In and of itself, the focal length change can affect theimaging properties (e.g., depth of focus, depth of field, aliasingproperties, aberration tolerance) of the optical system—which may not bedesired. Accordingly, the motor and controller may additionally move theoptical filter(s) so as to modify phase of the wavefront, to readjustthe imaging properties so that they remain unchanged even with thechange of focal length. In this way, for example, one can maintain adepth of field in object space irrespective of a change of focal length.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 shows one optical imaging system with mechanical adjustmentof a phase filter;

[0025]FIGS. 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H illustrate phase forms,surface configurations, and/or mechanical motions for exemplary phasefilters;

[0026]FIG. 3 shows one optical imaging system with mechanical adjustmentof optical phase filters;

[0027]FIG. 4 shows the optical imaging system of FIG. 3 with a postprocessor;

[0028]FIG. 5 shows the optical imaging system of FIG. 3 with a userinterface and housing;

[0029]FIG. 6 shows one control process exemplifying operation of theoptical system of FIG. 5;

[0030]FIG. 7 shows one exemplary phase mask having variations inthickness; and

[0031]FIG. 8 shows one optical imaging system with mechanical adjustmentof phase filters utilizing linearization for images detected by anon-linear analog detector.

DETAILED DESCRIPTION OF THE INVENTION

[0032]FIG. 1 shows one optical system 10 that selectively obtainsdesired imaging properties (e.g., depth of field, aberration tolerance,anti-aliasing) through wavefront coding and mechanical adjustment.Wavefront coding occurs through operation of optical phase filter 14,which is for example a phase mask that employs aspheric surfaces tomodify phase of a wavefront 15 between object 12 and detector 18. Optics16 (e.g., lenses and/or mirrors) operate to focus wavefront 15 todetector 18, as shown.

[0033] Detector 18 digitally captures the focused electromagneticradiation of wavefront 15. A digital image processor 20 post-processesdata 19 from detector 18 to “undo” certain effects induced by opticalphase filter 14, to obtain the desired imaging properties (e.g., toincrease in the depth of field of imaging system 10, to decrease inwavelength sensitivity, to change aliasing effects, and/or to changetolerance of optics 16 to misfocus-related aberrations). To “undo” thecertain effects, digital image processor 20 removes the spatial blurgenerated by aspheric phase filter 14; at the same time, optics 16 andphase filter 14 operate to ensure that the spatial effects aresubstantially constant over the range corresponding to the desiredimaging properties. Image processor 20 effectively performs a reverseconvolution with the spatial blur generated by phase filter 14,utilizing other system parameters as needed and desired to change orenhance the imaging properties. System 10 thus produces a final image 22with these desired image properties (e.g., a clear image over a selecteddepth of focus) as described in more detail below.

[0034] Wavefront coding element 14 is positioned, rotated and/ortranslated within optical system 10 by a motor and controller 30 toeffect desired phase modification of wavefront 15. Through feedback 32with motor and controller 30, digital image processor 20 has positionalinformation of optical phase filter 14; this information is utilizedwithin digital image processor 20 to “undo” the spatial effects inducedby optical phase filter 14 on the image formed at the detector 18.

[0035] In one embodiment, optical phase filter 14 is at an aperture ofoptical imaging system 10 (or at an image of the aperture), such thatthe point spread function (PSF) of system 10 is substantiallyinsensitive to misfocus and such that the optical transfer function(OTF) of system 10 has no zero-value regions within the passband ofdetector 18. Because the OTF is devoid of zero value regions, digitalimage processor 20 may obtain final image 22 by undoing the spatialeffects of optical filter 14. Since the OTF is insensitive to misfocus,digital image processor 20 generates final image 22 with the desiredimaging properties. U.S. Pat. No. 5,748,371 describes wavefront codingto extend depth of field and is incorporated herein by reference.

[0036] Through operation of motor and controller 30, optical phasefilter 14 may also be positioned within system 10 at a principal plane(or image of the principal plane), at an aperture stop (or image of theaperture stop), and/or at a lens (e.g., with optics 16). Suchpositioning ensures that imaging system 10 minimizes vignetting. In oneembodiment, optical phase filter 14 modifies only phase of the wavefrontbetween object 12 and detector 16 so as to minimize energy losses withinsystem 10. Those skilled in the art appreciate that filter 14 may beincorporated with optics 16 (e.g., as a wavefront encoded surface of anoptical element representing optics 16).

[0037] As described earlier, motor and controller 30 positions, rotatesand/or translates optical phase filter 14 within system 10. FIGS. 2A,2B, 2C, 2D, 2E and 2F illustrate various exemplary mechanical movementsand configurations of filter 14 relative to the optical footprint 40 ofwavefront 15 at filter 14. For example, in one embodiment illustrated inFIG. 2A, motor and controller 30 positions filter 14A within system 10in the pathway of wavefront 15 (position A, FIG. 2A), and alternativelypositions filter 14A out of the pathway of wavefront 15 (position B,FIG. 2A) by translational movement 42. In such an embodiment, filter 14Atherefore affects wavefront 15 in position A, and has no effect on thewavefront in position B.

[0038] Those skilled in the art appreciate that another like filter 14Amay also be included within a system of this embodiment so as toprovide, for example, two phase states of wavefront 15. In a first phasestate, wavefront 15 is affected by two filters 14A (both in position A);in a second phase state, wavefront 15 is affected by one filter 14A (onefilter 14A in position A, the other filter 14A in position B).

[0039] In another embodiment shown in FIG. 2B, motor and controller 30translates optical phase filter 14B transverse to optical axis 17 (e.g.,perpendicular to axis 17), along movement direction 44, to modify phaseof wavefront 15 in at least two different positions of transversemovement 44. For example, the phase modification of wavefront 15, byfilter 14B, is different at position A within FIG. 2B as compared toposition B. For example, the phase function implemented within filter14B is different depending upon whether footprint 40 is at position A orposition B.

[0040] In yet another embodiment shown in FIG. 2C and FIG. 2D, motor andcontroller 30 rotates filter 14C (rotational movement direction 46) in aplane relative to optical axis 17 (e.g., the plane may for example beperpendicular to axis 17) to modify phase of wavefront 15 as a functionof rotational position (0, or “theta”). FIG. 2D illustrates that twolike filters 14C(1), 14C(2) may be similarly positioned along opticalaxis 17; motor and controller 30 then operates, for example, to rotatefilters 14C in opposite rotational directions 46(1), 46(2), as shown.

[0041] In a similar embodiment shown in FIG. 2E, motor and controller 30translates filters 14E(1), 14E(2) in transverse motions 44E(1), 44E(2),respectively, to generate the desired phase effect on wavefront 15. Oneor both of filters 14E may be moved at any one time, depending upon thephase function of these filters.

[0042] In yet another embodiment, two phase filters 14F(1), 14F(2) areshown along optical axis 17 in FIG. 2F. In this configuration, motor andcontroller 30 may move one or both of filters 14F along direction 48 tovary the combined wavefront phase caused by filters 14F. In anotherembodiment, motor and controller 30 operate to tilt (e.g., alongdirection 49) one or both of filters 14F to provide desired phase changethrough the pair of filters 14F, thereby “encoding” wavefront 15 in away so as to achieve the desired image properties.

[0043]FIG. 2A-2F also illustrate that phase filter 14 may take variousphysical forms (e.g., rectangular, FIG. 3B, or circular, FIG. 2A andFIG. 2C) without departing from the scope hereof.

[0044] Accordingly, in one embodiment, the phase function of opticalfilter 14 is designed to induce the desired phase change of wavefront 15according to the motion (e.g., movement directions 42, 44, 46, 46(1) and46(2), 44E(1) and 44E(2), 48 or 49) of motor and controller 30, such asdescribed below in connection with FIG. 3-FIG. 6.

[0045] For example, the phase function P (equivalent to surface height)of filter 14C(1) and 14C(2) may for example take the phase form ofEquation 1:

P(r,theta)=A(r)*Sum[a _(i) cos(w _(i) theta+phi_(i))]+B(r)  (Eq. 1)

[0046] where r denotes the filter radius value and theta denotes thefilter angular coordinate. The summation (sum, or Σ) is over the index iand A(r) is a function of r multiplied by a function that is a sum ofcosine terms. The composite phase modification of wavefront 15 passingthrough both filters 14C(1), 14C(2) is then shown in Equation 2, that ismotor and controller 30 adjusts phase of wavefront 15 according torotational movement of filter 14C(1) and 14C(2) about optical axis 17.In particular, assume for example that only one term of the cosinesummation is used. If delta is zero, filters 14C(1), 14C(2) areperfectly aligned. Motor and controller 30 thus operates to rotatefilters 14C(1), 14C(2) as a function of delta. With equal and oppositerotations (plus and minus delta, respectively) of filters 14C(1),14C(2), the combined phase becomes: $\begin{matrix}\begin{matrix}{{P_{c}\left( {r,{theta}} \right)} = {\left\{ {{Phase}\quad {of}\quad {filter}\quad 14\quad {C(1)}\quad {with}\quad {rotation}\quad {of}\quad \left( {+ {delta}} \right)} \right\} +}} \\{\left\{ {{Phase}\quad {of}\quad {filter}\quad 14\quad {C(2)}\quad {with}\quad {rotation}\quad {of}\quad \left( {- {delta}} \right)} \right\}} \\{= {\left( {{{A(r)}*{\cos \left( {{w*{theta}} + {delta}} \right)}} + {B(r)}} \right\} +}} \\{\left\{ {{{A\left( {r,{theta}} \right)}*{\cos \left( {{w*{theta}} - {delta}} \right)}} + {B(r)}} \right\}} \\{\left. {= {{A(r)}*{\cos\left\lbrack {{w*{theta}} + {delta}} \right.}}} \right) +} \\{\left. {\cos \left( {{w*{theta}} - {delta}} \right)} \right\rbrack + {2*{B(r)}}} \\{= {{2*{\cos ({delta})}{A(r)}{\cos \left( {w*{theta}} \right)}} + {2*{B(r)}}}}\end{matrix} & \left( {{Eq}.\quad 2} \right)\end{matrix}$

[0047] Accordingly, the combined phase (e.g., affecting the amount ofvariation within the depth of field) is modulated by different rotations46 by motor and controller 30, affecting delta through the termcos(delta) of Eq. 2. For rotation values where delta=90 degrees, thecombined phase of the non-rotationally symmetric term can be reduced tozero. At this value of delta, the wavefront is minimally modified andthe amount of extended depth of field, aberration tolerance,anti-aliasing, etc., is also minimized. For rotation values of deltathat are multiples of 360 degrees, the combined phase of thenon-rotationally symmetric term is maximized; at these values of delta,the amount of extended depth of field, aberration tolerance, andanti-aliasing are also maximized. The rotationally symmetric componentB(r) is unchanged in form, and is optional. The cosine terms can bereplaced by sums of cosines and hyperbolic functions with equivalentresult.

[0048] A side view of filters 14C(1), 14C(2) is shown in FIG. 2G. FIG.2G is shown to illustrate that in the above example of Equation 2, thephase form (Eq. 1) of filters 14C occurs on the first side 21 of eachfilter 14, each facing upstream from detector 18, as shown.

[0049] In another example, the phase function P (equivalent to surfaceheight) of filters 14E(1), 14E(2) may for example take the followingform:

P(x,y)=alpha {x ⁴ +y ⁴}  (Eq. 3).

[0050] where x and y are Cartesian coordinates of the phase function onfilters 14E. The phase of wavefront 15 is encoded by passing through thepair of filters 14E according to translational movements delta 44E(1),delta 44E(2), respectively, of filters 14E. Motor and controller 30controls the transverse motion delta 44E(1), 44E(2) along the x=ydirection (along a 45 deg. angle), to selectively adjust the phasemodification of wavefront 15. With motion along the x=y direction, forexample, the wavefront phase is altered in both the x and y directionsas a function of motion delta 44E (equal but opposite motions delta44E(1) and 44E(2) occurring simultaneously). The combined phaseimplemented by the collection of filters 14E(1) and 14E(2) is then:$\begin{matrix}\begin{matrix}{{P_{c}\left( {x,y} \right)} = {\left\{ {{Phase}\quad {of}\quad {filter}\quad 14{E(1)}\quad {with}\quad {translation}\quad {of}\quad \left( {+ {delta}} \right)} \right\} -}} \\{\left\{ {{Phase}\quad {of}\quad {filter}\quad 14\quad {E(2)}\quad {with}\quad {translation}\quad {of}\quad \left( {- {delta}} \right)} \right\}} \\{= {{{alpha}\left\{ {\left( {x - {delta}} \right)^{4} + \left( {y - {delta}} \right)^{4}} \right\}} -}} \\{{{alpha}\left\{ {\left( {x + {delta}} \right)^{4} + \left( {y + {delta}} \right)^{4}} \right\}}} \\{= {{- 8}\quad {alpha}\left\{ {{{delta}*\left( {x^{3} + y^{3}} \right)} + {{delta}^{3}*\left( {x + y} \right)}} \right\}}}\end{matrix} & \left( {{Eq}.\quad 4} \right)\end{matrix}$

[0051] The phase of filter 14E(2) is the negative of the phase of filter14E(1) in this example. Accordingly, by moving filters 14E(1), 14E(2) inequal but opposite directions, one provides positive phase change andone provides negative phase change. Notice that in this example phaseform of the combined filters is a scaled cubic form (delta*(x³+y³)) anda linear phase component (delta³*(x+y)). By changing the translationdelta 44E (i.e., controlled by motor and controller 30 along a line ofx, y), the amount of cubic phase (and a corresponding amount of desiredimaging property, e.g., depth of field) can be varied. This translationalso brings with it a linear phase, prism-like optical axis or imageorigin translation. So, in eq. 4, the first term is like a separablecubic and the second term is linear term similar to a prism effect (ortilt). The translation can be used as is, or the mechanism thattranslates the component parts can be such that the component partsphysically tilt away from optical axis 17 (see FIG. 2F) with translationto the complement of the linear phase; more terms may be added to theoptical surfaces to purposely remove tilt.

[0052] A side view of filters 14E(1), 14E(2) is shown in FIG. 2H. FIG. 2GH is shown to illustrate that in the above example of Equation 4, thephase form (Eq. 3) of filters 14E occurs on the first side 23A of filter14E(1) and the second side 23B of filter 14E(2), as oriented to detector18, as shown. By reversing the directions of these filters, the phase ofone can be the negative of the phase of the other.

[0053] It should be clear to those skilled in the art that phase filter14 modifies wavefront 15 so that there is not an ideal focus at detector18; each object point of object 12 is instead spatially blurred over anextended range about along axis 17. This blurring “encodes” wavefront 15from object 12 to detector 18; digital imaging processor 20 then“decodes” the image from detector 18 according to the position of phasefilter 14 (via feedback 32) to generate an enhanced final image 22.Image 22 is “enhanced” for example since it has a selected depth offocus. Image 22 may be further enhanced since it is selectivelyinsensitive to certain optical aberrations, for example misfocus-relatedaberrations such as chromatic aberration, curvature of field, sphericalaberration, astigmatism, and/or temperature, or pressure relatedmisfocus associated with plastic optics. As such, optics 16 mayadvantageously employ plastic.

[0054] Moreover, detector 18 may create aliasing, such as when detector18 is a CCD array. Accordingly, in one embodiment the phase function ofphase filter 14 provides low-pass filtering to selectively inhibiteffects of such aliasing as an enhancement to final image 22.

[0055] In one embodiment, motor and controller 30 also controls theaperture of system 10. By way of example, system 10 may include anelectronically-controllable aperture 31 which responds to motor andcontroller 30 to adjust the aperture of system 10. When aperture 31 isadjusted, therefore, the depth of field (or depth of focus) changes.Accordingly, motor and controller 30 may additionally move phase filter14 to adjust the depth of focus (or depth of field) so as to maintainconstant image properties irrespective of the change of aperture 31, ifdesired. In a similar way, aberration tolerance and/or aliasingproperties of system 10 may be adjusted to compensate for aperturevariation. Digital image processor 20 may also utilize the aperture sizeinformation during processing by virtue of feedback 32.

[0056] In one embodiment, motor and controller 30 also controls thefocal length of system 10. By way of example, motor and controller 30may move optics 16 to effect the focal length adjustment. When the focallength is adjusted, therefore, the depth of field (or depth of focus)changes. Accordingly, motor and controller 30 may additionally movephase filter 14 to adjust the depth of focus (or depth of field) so asto maintain constant image properties irrespective of the change offocal length, if desired. In a similar way, aberration tolerance and/oraliasing properties of system 10 may be adjusted to compensate for focallength variation. Digital image processor 20 may also utilize the focallength information during processing by virtue of feedback 32.

[0057]FIG. 3 shows one optical imaging system 100 with an extended depthof field through operation of mechanically-adjustable optical phasefilters 102, 104. An object 50 generates or reflects electromagneticradiation 52 that is captured by optics 106 of imaging system 100 toimage object 50 to a detector 108; this imaging forms an opticalwavefront 101 (illustrating points of constant phase from object 50)that passes through filters 102, 104. The depth of field of imagingsystem 100 is “enhanced” as compared to the same imaging system withoutfilters 102, 104, as described in more detail below. In one embodiment,one or both of filters 102, 104 include aspheric optical elements. Thoseskilled in the art appreciate that although only two filters 102, 104are shown, additional filters may be included without departing from thescope hereof.

[0058] Filters 102, 104 may move by operation of motor and controller116. When motor and controller 116 moves filters 102, 104, the phase ofwavefront 101 is modified to accomplish one or more of the following:modify the depth of field of imaging system 100, modifyaberration-tolerance of imaging system 100, and modify anti-aliasingeffects of detector 108. In one embodiment, such mechanical adjustmentis effected by rotating one or both of filters 102, 104 about opticalaxis 103. To enhance the depth of focus, phase filters 102, 104 aremoved to alter the optical transfer function (OTF) of system 100 (andspecifically of optics 106) such that the resulting OTF is substantiallyinsensitive to misfocus-related aberrations over a greater range ofaberrations as compared to aberrations of optics 106 without filters102, 104. In one embodiment, the variation of OTF is chosen by varyingthe amount of rotation of one phase filter 102 with respect to the otherphase filter 104.

[0059] In one arrangement, phase filter 102 and phase filter 104 areplaced at or near the aperture stop (or at an image of the aperturestop) of optical system 100, and one filter 104 is rotated relative tofilter 102 (or vice versa). Filters 102, 104 may alternatively bepositioned at a principal plane (or at an image of the principal plane)of system 100, or at a lens (e.g., at an optical element of optics 106).Although filters 102, 104 are shown adjacent to one another, in filters102, 104 may be spaced apart from one another (one or both being on oroff of axis 103) so long as they cooperate to change phase of wavefront101 (when positioned by motor and controller 116). In one arrangement,filters 102, 104 are configured such that as one filter rotates, theother filter has an equal and opposite rotation to effect the phasemodification onto wavefront 101.

[0060] Detector 108 detects focused electromagnetic radiation ofwavefront 103 to form a final image 110, which is a digitalrepresentation of object 50. Electromagnetic radiation 52 may includeelectromagnetic radiation in the visible spectrum, but may also includeelectromagnetic radiation in the infrared spectrum, ultravioletspectrum, radio wave spectrum, or other spectrum (or mixtures thereof).Detector 108 may be analog detector (e.g., photographic film) or digitaldetector (e.g., a CCD or CMOS array).

[0061]FIG. 4 shows optical imaging system 100 with a post processor 112,for example a digital filter, that performs post-processing on the imagedetected by detector 108 to form a final image 114. Post processor 112removes certain effects of wavefront coding induced by filters 102, 104to form final image 114, for example to provide a sharp and in-focusimage. Optical system 100 is thus particularly well suited for use indigital imaging systems, such as digital cameras, because of the linearresponse of detector 108 in the form of a digital detector.

[0062] Rotation of filters 102, 104 (e.g., each moving as in direction46, FIG. 2C) may occur through operation of a motor and controller 116;motor and controller 116 may operate automatically or in response touser commands. Those skilled in the art appreciate that filters 102, 104may instead be manually adjusted and/or rotated. In one embodiment,initial manual adjustment occurs during assembly of optical system 100,and further operational adjustment occurs by operation of motor andcontroller 116, providing a large range of phase modification forwavefront 101.

[0063] Optical system 100 may also allow for selective control offocusing, magnitude of the depth of field, and/or aberration reduction.More particularly, FIG. 5 shows one housing 118 that may encasecomponents of system 100. A user interface 120 mounts with housing 118,as shown. User interface 120 is in electrical communication with acontroller 122 (e.g., a microprocessor) to control operation of motorand controller 116, in response to user commands at interface 120, so asto control positioning of filters 102, 104 (to effect phase modificationof wavefront 101). Those skilled in the art appreciate that controller122 may be part of motor and controller 116 as a matter of designchoice. In one embodiment, controller 122 receives information 117 frompost processor 112, the information for example detailing presence ofmisfocus and/or aberrations in final image 114. In one example,information 117 is used by controller 122 to direct motor and controller116 to move filters 102, 104 and modify phase of wavefront 101, such asto control depth of field and aberration tolerance within system 100.This control then adjusts the image quality of final image 114.

[0064]FIG. 6 shows one process 200 facilitating operation of opticalsystem 100, FIG. 5. In step 202, a user makes selections on userinterface 120 regarding desired focusing, degree of depth of field,amount of anti-aliasing and/or aberration reduction within system 100.In response to user selection, a signal is generated and communicated tocontroller 122. In step 204, controller 122 generates a command signalfor communication to the motor and controller 116. Motor and controller116 then positions (e.g., rotates, translates, repositions) one or bothof filters 102, 104, in step 206. Detector 108 then captures the imageof wavefront 101, in step 208. In step 210, post processor 112 receivesdata from detector 108 and processes the data to reverse effects inducedby filters 102, 104, to form final image 114 with user-selected imagingproperties (e.g., depth of field, reduced aberrations, anti-aliasing).

[0065]FIG. 7 shows one phase form 202 of wavefront filters 102, 104 thatmay be used in optical system 100. Phase form 202 includes a body 204 ofoptical material having variations in thickness that induces phasechange on wavefront 101. In one embodiment, form 302 implements a cubicphase function given by:

P(x,y)=αx ³ +βy ³ +δx ² y+γxy ²  (Eq. 5)

[0066] where P(x,y) represents the phase function of filters 102, 104 asa function of spatial coordinates (x,y), where (x,y) is the displacementlocation of form 202 from optical axis 103 (e.g., in FIG. 7 only axis xis shown). The constants α, β, δ, and γ are chosen according to theparticular characteristics desired for optical system 100. For example,with α=β, and δ=γ=0, a rectangularly separable optical filter is formed.This leads to rectangularly separable processing within digital signalprocessor 112 in controlling depth of field and aberrations.

[0067] Another phase function for form 202 provides an MTF that iscircularly symmetric. The wavefront phase of the optical filter can bewritten in polar coordinates as:

P(r,θ)=αf(r)cos(nθ)  (Eq. 6)

[0068] where f(r) is a function dependent upon radial position r from acenter of the phase function and θ is angular position about the center.By way of example, one phase function P(r,θ) is a r³ cos(3θ), where f(r)is r³ and n is 3 (which also corresponds to Eq. 5 with the constantschosen as α=β, δ=γ=−3α). The magnitude of the constant α determines theamount of phase change implemented by filter(s) 102, 104, thus providingthe selected imaging properties (e.g., depth of field,aberration-tolerance, or anti-aliasing).

[0069] If two wavefront filters of the form of Eq. 6 are placed adjacentto and parallel to each other with the optical centers of each (r=0) ator near optical axis 103, the effective phase from the combination canbe approximated as:

P(r,θ)_(c) =f(r)[cos(n{θ−φ})+cos(n{θ+φ})]  (Eq. 7)

[0070] where each filter has been rotated an equal and opposite amountgiven by angle φ. In such a configuration, only the relative angularposition between the two wavefront filters is important. This particularsymmetric alignment of Eq. 7 is used only to illustrate simplifiedmathematics. The form of the combination wavefront phase of Eq. 7 can befurther simplified to:

P(r,θ)_(c)=[2 cos(3φ)]f(r)cos(3θ)  (Eq. 8)

[0071] The phase of the combination is seen to vary between twice thephase of a single surface (when φ=n(π/3), n=0, +/−1, +/−2, . . . ) tozero or a constant surface (when φ=n(π/6), n=+/−1, +/−2, . . . ) throughchange of the relative rotation between the filters 102, 104. If therotation orientation of one of the filters is reversed, the phase isdescribed by the addition of a negative sign, equivalent to a differentrotation.

[0072] Other general phase forms may be described in polar coordinates,such as:

P(r,θ)=cos(nθ) A(r,θ)+B(r)  (Eq. 9)

[0073] where A(r,θ) and B(r) are functions of the radius (from opticalaxis 103) and θ, and cos(nθ) provides a non-rotationally symmetricrotational variation in the phase. The second term describes the generalcase, including displacement. For example, by fabricating the filterdescribed by Eq. 6 onto the surface of a lens (e.g., form 202, FIG. 6),A(r,θ) is equal to a r³ cos(3θ) and B(r) is equal to φr², where φdescribes the power of the lens.

[0074] From Eq. 8, placing two filters of the form of Eq. 9 adjacent toand parallel to each other, with equal and opposite rotations of φ,results in a combined wavefront phase that can be approximated as:

P(r,θ)_(c)=[2 cos(nφ)]A(r)cos(nθ)+2B(r)  (Eq. 10)

[0075] The rotationally symmetric component B(r) is unchanged byrotations while the non-rotationally symmetric combined wavefront phasecan vary between twice that of a single element and zero depending onthe relative rotation of the two filters.

[0076] The magnitudes of the non-rotationally symmetric components ofthe filters do not have to be identical. In such cases, the range ofwavefront phase possible through rotation can be reduced. Therotationally symmetric terms B(r) also do not have to be identical.

[0077] Those skilled in the art appreciate that other phase functionsmay be implemented with filters 102, 104 depending on the desiredoptical imaging properties for system 100. Moreover, phase filters 102,104 may include reflective elements, holographic elements, elementsincluding variations in index of refraction, spatial light modulators,holograms, adaptive optics, diffractive elements such as modulo Nπmasks, and/or the like.

[0078]FIG. 8 shows one optical system 400 similar to optical system 100of FIGS. 3 and 4, with optics 406, a first aspherical optical wavefrontfilter 402, a second aspherical optical wavefront filter 404, anon-linear analog detector 408 and post processor 412, as well asautomatic motor and controller 416. Wavefront 403 is formed fromelectromagnetic radiation 52 from object 50 and is focused by optics 406through wavefront filters 402, 404 and to analog detector 408. Automaticmotor and controller 416 rotates one or more of wavefront filters 402,404 to effect mechanical adjustment of the wavefront phase. However,because of the non-linearity of analog detector 408—in that detector 408has a non-linear response to the intensity of wavefront 52—postprocessor 412 cannot perform the function of removing wavefront codingor spatial blur induced by wavefront filters 402, 404 to produce a sharpand in-focus final image 414. For non-linear analog detectors 408, sucha photographic film, the exposure curve is generally known or can bemeasured. Thus, the images detected by analog detector 408,representative of wavefront 402, may be linearized. Non-linear analogdetector 408 is thus digitally scanned to generate a representation 418of the image. The scanned representation 418 is then linearized to forma linearized image 420. Post processor 412 (e.g., a digital filter)processes linearized image 420 in much the same way as post processor112 processes image 420 to remove effects of wavefront filters 102, 104,to increase depth of field (depth of focus) in final image 414.

[0079] Since certain changes may be made in the above methods andsystems without departing from the scope hereof, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing be interpreted as illustrative and not in a limiting sense. Itis also to be understood that the following claims are to cover certaingeneric and specific features described herein.

1. An optical imaging system to variably control image properties of animage, comprising: at least one optical phase filter; and a controllerfor positioning the optical phase filter to alter phase of a wavefrontof the imaging system to select the properties of the image.
 2. Theoptical imaging system of claim 1, the image properties comprising oneor more of depth of focus, aberration tolerance and aliasing properties.3. The optical imaging system of claim 1, the at least one optical phasefilter comprising first and second optical filters.
 4. The system ofclaim 1, the optical phase filter comprising a circularly symmetricphase form of P(r,θ)=A(r,θ)+B(r).
 5. The optical imaging system of claim4, the optical phase filter comprising aspheric optical elements.
 6. Theoptical imaging system of claim 1, the controller comprising a motor. 7.The optical imaging system of claim 1, the controller translating theoptical phase filter between at least two positions wherein thewavefront passes through at least two separate portions of the opticalphase filter.
 8. The optical imaging system of claim 1, the controllerrotating the optical phase filter about an optical axis to effect phasechanges to the wavefront.
 9. The optical imaging system of claim 1, theoptical phase filter having a phase function of the form P(x,y)+D(x₁,y₁).
 10. The optical imaging system of claim 1, the optical phase filterbeing disposed proximal to one of an aperture stop of the optical systemand an image of the aperture stop. 11 The optical imaging system ofclaim 1, further comprising (a) a detector for capturing an image of theobject and (b) a post processor for processing data from the detector toreverse effects induced by the optical phase filter.
 12. The opticalimaging system of claim 11, wherein the post processor comprises adigital filter.
 13. The optical imaging system of claim 1, furthercomprising a user interface for selecting magnitude of at least one ofthe image properties and a controller, responsive to user selections atthe interface, to direct the controller to position the optical phasefilter and affect the magnitude.
 14. The optical imaging system of claim1, wherein the controller comprises an automatic motor and controller.15. The optical imaging system of claim 1, wherein the optical phasefilter is disposed proximal to one of an aperture stop of the opticalsystem and an image of the aperture stop.
 16. The optical imaging systemof claim 1, wherein the optical phase filter comprises a phase mask. 17.The optical imaging system of claim 18, wherein the phase maskimplements a phase function of the form: P(r,θ)_(c)=[2 cos(3φ)]αr ³cos(3θ).
 18. The optical imaging system of claim 18, wherein the phasemask implements a cubic phase function when moved by the means formoving.
 19. The optical imaging system of claim 18, wherein the cubicphase function is of the form: P(x,y)=αx ³ +βy ³ +δx ² y+γxy ² whereP(x,y) represents phase as a function of the spatial coordinates (x,y).20. The optical imaging system of claim 1, the characteristics of theimage comprising one or more of depth of focus, depth of field, aliasingproperties, and aberration tolerance.
 21. The optical imaging system ofclaim 1, further comprising means for adjusting one or both of apertureand focal length of the system, the controller repositioning the opticalphase filter so that the imaging properties remain substantially fixedirrespective of the means for adjusting.
 22. A method for variablyaffecting the wavefront of an optical system to selectively controlimaging properties, the method comprising the steps of: positioning oneor more optical phase filters in the optical system; and repositioningthe optical phase filters to affect the imaging properties.
 23. Themethod of claim 22, further comprising the step of capturing images fromthe system and post-processing a digital representation of the images toreverse effects induced by the optical phase filters.
 24. The method ofclaim 23, further comprising the steps of automatically responding touser selection of the imaging properties to reposition the optical phasefilters to effect phase changes of the wavefront to achieve the selectedimaging properties.
 25. The method of claim 22, further comprisingadjusting one or both of focus and aperture of the imaging system, thestep of repositioning comprising repositioning the optical phase filtersto counter imaging effects associated with the step of adjusting one orboth of focus and aperture.
 26. A method for variably affecting thewavefront of an optical system to select image properties of the opticalsystem, the method comprising the steps of: moving a phase filter withinthe optical system to modify phase of the wavefront; and forming a finalimage by post processing data from a detector of the optical system toreverse effects induced by the phase filter and achieve the selectedimage properties.
 27. The method of claim 26, further comprising thestep of modifying one or both of a focal length and aperture of theoptical system, the step of moving comprising the step of moving thephase filter to compensate for modification of the focal length andaperture such that image properties remain substantially unchanged. 28.The method of claim 27, the image properties comprising one or more ofdepth of field, aberration tolerance and aliasing properties.
 29. Amethod for variably affecting the wavefront of an optical system toselect image properties of the optical system, the method comprising thesteps of: moving at least two phase filters within the optical system tomodify phase of the wavefront; and forming a final image by postprocessing data from a detector of the optical system to reverse effectsinduced by the phase filters and achieve the selected image properties.